Collection of hard data on the effects of liberalized abortion in the United States is handicapped by the absence of a uniform national reporting system, the difficulties of obtaining a representative sample amidst diverse abortion facilities, and the low probability of adequate follow-up. For example, information is lacking on abortion effects on subsequent pregnancies and deliveries, contraceptive practice and vigilance, repeat abortion, abortion and contraceptive counseling and the decision-making process leading to contraception, abortion, and repeat abortion under differing circumstances. It is possible to obtain such information reliably, readily, and economically in Denmark, a country whose social structure and fertility-regulating history are so similar to the United States' as to provide a good indicator of what to expect. The liberalized statute of October 1973 provides abortion free on request up to 12 weeks of pregnancy. The procedure must be performed in a hospital and is fully recorded in the Central Abortion Registry, together with the woman's unique Person Number, which provides entry to the continuously updated National Population Registry and the several associated registries of the National Board of Health and Birth Registry. It is proposed to extend an already initiated and funded study by following at six-month intervals over a two-year period a total of 8,000 women, divided into four groups, residing in urban and rural areas, who, during the previous year, either had an induced abortion, delivered a full-term pregnancy, had a spontaneous abortion, or had no pregnancy. The international abortion research experience of the Transnational Family Research Institute will be associated with that of the Joint Center for the Study of Health Programs established at the University of Copenhagen. Through the unique Danish registration systems and with the assistance of trained interviewers, we expect to obtain a better understanding of the decision-making process when both modern contraceptives and safe abortions are readily available and reliable information on the effects of liberalized abortion, data unlikely to be obtainable at reasonable costs for some time in the U.S.